Manufacture of petroleum coke



United States Patent 0 3,116,231 MANUFACTURE @F RETROLEUM Ct'BKELawrence E. Adee, Mapieweod, La, assignor to ontiuental Gil Company,Pouca City, Okla, a corporation of Delaware Filed Aug. 22, 1%43, Ser.No. 59,959 7 Claims. (Cl. 208-46) This invention relates to themanufacture of petroleum coke. More particularly, it relates to animpnoved process for the manufacture of petroleum coke wherein the cokefines produced during the process are recovered and recycled to thecoking step in order to increase yields and minimize the problem ofdisposing of such fines.

In the delayed coking process a petroleum fraction is heated to atemperature at which it will thermally decompose. The oil is then fedinto a drum under conditions which prevent the oil from vaporizing untilit has partially decomposed. This thermal decomposition produces a veryheavy tar which undergoes additional decomposition depositing a porouscoke mass in the drum.

In the usual application of the delayed coking process, residual oil isheated by exchanging heat with the liquid products from the process andis fed into a fractionating tower where any light products which mightremain in the residual oil are distilled out. The oil is then pumpedthrough a furnace where it is heated to the required temerature anddischarged into the bottom of the coke drum. The first stages of thermaldecomposition reduce this oil to a very heavy tar or pitch which furtherdecomposes into solid coke. The vapors formed during this decompositionproduce pores and channels in the coke thru which the incoming oil fromthe furnace may pass. This process is continued until the drum is filledwith a mass of coke. The vapors formed in the process leave from the topof the drum and are returned to the fractionating tower where 1 hey arefractionated into the desired cuts.

The attrition associated with removing petroleum coke from delayedcoking drums and the subsequent coke handling produces a considerableamount of undersized coke fines. Prior to development of this invention,these fines constituted a disposal problem. Their value as fuel is muchless than the value of the larger lumps of coke because of the limitedamount of line coke which can be utilized economically in the variousprocesses consuming petroleum coke.

This invention provides a method for recovering these fines andreturning them to the delayed coking unit where they are cemented into anew coke being produced in such a manner that they loose their identityand are subsequently recovered as part of the useful sized coke lumps.

Broadly stated, the invention is a process for producing petnoleum cokewhich comprises subjecting a heavy petroleum residuum to cokingconditions of temperature and pressure, recovering the coke fineproduced during the process, and injecting the recovered coke fines intothe coker feed. One preferred embodiment consists of slurrying the cokefines in a suitable oil, delivering the slurry to the coke drum wherethe coke particles become sus pended in the heavy tar or pitchundergoing thermal decomposition. Under these conditions, the cokeparticles become incorporated into the new coke being formed so thatthey become an integral part of the coke deposit.

The coke fines to be handled by this invention may be either wet or dry.It will normally not be necessary to dry the wet fines except to decantthe excess water from settled fines. It is true, however, that dry finesare easier to handle than wet fines.

ice

Any suitable oil can be used for the initial slurry.

Normally it will be one of the oil streams available from the cokingunit. While the residual oil feed to the unit is appropriate, wepreferto use gas oil merely for the sake of convenience. Engineeringfactors determine the proper point for inecting the slurry into a givendelayed coking unit. The ma or factors to be considered are heatrequirements, fluid velocity, abrasion of equipment, and equipmentfouling. The more important locations to be considered tor inecting theslurry are:

(l) The slurry may be injected directly into the coke drum either withor Without prior heating.

(2) The slurry may be injected into the furnace feed line.

(3) The slurry may be injected into the fractionator tower.

(4) The slurry may be injected into the feed stream as it enters theexchanger train.

Selection of suitable charge stocks for coking operatlons is well knownin the art. The principal charging stocks are high boiling virgin orcracked petroleum residua such as: virgin reduced crude; bottoms fromthe vacuum distillation of reduced crudes, hereinafter referred to asvacuum reduced residuum; Duo-sol extract; thermal tar; and other heavyresidua. Blends of these materials are often used to provide a feedwhich will provide a suitable coke having a sufiiciently low sulfurcontent.

As indicated above, the preferred coking process is the wellknowndelayed coking process. In this process, which is one of the mostcommonly-used and most economical at the present time, the charge stockis pumped at 150 to 500 psi. into a furnace where it is preheated to 850to 950 F. and then discharged into a vertical coking drum through aninlet at the base. The pressure in the drum is maintained at 20 to 80p.s.i., and the drum is well insulated to minimize heat loss, so thatthe reaction temperature lies between about 830 F. and 900 F. The hotcharge stock decomposes over a period of several hours, liberatinghydrocarbon vapors which rise through the mass continuously, stirringthe contents of the coker vigorously.

After removing the coke from the drum (usually by means of a high impactwater jet), the coke is broken into lumps and may be calcined, genenallyat a temperature of 1000 C. to 1500 C.

The preferred mode of operation is illustrated in the drawing. The freshfeed from line it is stripped in steam stripper 2, in which the feed issplit into two streams 3 and i, which are introduced into fraotionator5. The overhead from the fractionator, at about 300 F., is passed to thereflux drum 6, and a portion of the light ooker gasoline therefrom isrefluxed through line 55. l'laphtha is removed through line 9, a portionthereof being refluxed (not shown) from a naphtha stripper (not shown),if desired.

Gas oil is removed from the fractionator through line lit, and portionsthereof are refluxed by means of lines it and 12. The bulk of theremainder of the gas oil is removed at 13, but :a small quantity fromline 14 is used to form a slurry of coke fines for injection into thecoker, as will be described hereinafter.

The bottoms from the fractionator, at are passed through heater 1 .5,and then into one or the other of coke drums l6 and 17 at a temperatureof about 910 F. at the beginning of the coke run and about 925 F. at theend of the run. A stream of vapor, at about about 550 F,

839 F. and about 39 p.s.i.g., is recycled to the fractionator throughline 18.

When the coke drum is full, the coke is cooled and then removed from thedrum by means of high impact-producing water jets incorporated inspecial boring and cutting tools. After the raw coke is dewatered, it isthen crushed and screened to 1 /2 inches and smaller, and is then passedto raw coke storage silo 19.

The coking operations thus described (except the above eference to theuse of gas oil stream '14) comprise the standard coking process known asdelayed coking, and no claim to novelty is made thereto.

Coke is fed from the silo by gravity feed into feed end housing 29 andfrom there into inclined rotary kiln 21, in which the coke is calcinedat a temperature of about 2590" Coke passes downwardly through kiln 21,while hot gases pass upwardly through the kiln and countercurrent- 13 tothe flow of coke. The hot gases are created partially by combustion offuel gas introduced at 22. Primary and secondary sources of air aresupplied through lines 23 and 24, aifording an excess of air over thatrequired to combust the fuel gas introduced at 2 2. Hot gases are alsocreated by combustion of the volatile hydrocarbons from the raw cokewith the excess air. In normal operations, the combustion of thesevolatile hydrocarbons with the excess air affords approximately 69-70percent of the heat required to maintain the kiln temperature.

The calcined coke is removed from the lower end of the kiln at 25 and iscooled and then conveyed to storage.

The hot gases, containing coke fines, after passing throwgh the .kiln,are removed through line 216 and intro duced to cyclone separator 27,which is a cylindrical vessel with a cone-shaped lower portion. Thegases are introduced horizontally and tangentially to the inside surfaceof the cyclone. The fines drop to the bottom, are cooled in cooler 28,and are elevated to fines storage bin 29. The preferred cyclone isreferred to as a hot cyclone because no water is injected into it;however, if desired, a wet cyclone may be employed wherein water isinjected into the cyclone to aid in the separation of fines from gas.

Cyclone separators are standard dust-collecting equipment and may bepurchased from a number of sources and may be adapted for use in theseparation of coke fines with relatively little effort in the line of enineering skill.

The gas is removed from the top of the cyclone and is passed, throughline 39, to an incinerator (not shown) and to a waste heat boiler (notshown).

Fines from the storage bin 29 are fed to slurry drum 3 1, which isequipped with a propeller-type agitator driven by motor 32. Gas oil fromfractionator is used to form a slurry of coke fines which is fed throughline 33 directly to the particular coke drum being charged. The slurryis preferably maintained at or below 40 percent fines. of the finesrecovered may be used without detrimental effect upon the quality of thecoke produced.

Fines from areas other than the cyclone 27 may also be recycled to thecoking operations. For example, wet fines resulting from the dewateringof the raw coke hydraulically removed from the coke drum may be dried ordrained of most of the water, slurried with oil, and then fed to thecoke drum as indicated above. Wet fines may oil, and the slurry boiledto remove the water, thus affording an oil slurry which may be indruni.Fines from the bottom of the feed end housing 29 may also be recycled tothe coking operations by the slurry method.

As an alternate to the slurry method, the dry fines may be introducedinto the coke drum as a fluidized solid by the use of superheated steam,or other suitable gas. Wet fines, from the hydraulic removal of cokefrom the drum, may first be dried in the carciner or other dryingequipment and recovered in the cyclone as previously described.

4 The following examples are :set forth to illustrate the invention, itbeing understood that they are not to be construed as limiting itsscope.

EXAlM-PLE 1 Nine pilot coking runs were performed using vacuum reducedresiduum as the coker feed stock having the following properties:

Fines previously recovered in a wet cyclone (located at the dischargeend of the rotary kiln) were first dried and were then slurried with thefeed prior to introduction into the coker.

The results of these runs are shown below in Table 1. It will the notedthat runs 1-4 were made without recycle, whereas runs 59 employedinjection or" fines.

Table I a Feed:

Wt. percent 100 100 100 97. 1 97.1 97.1 97.1 97.1

Pounds 39. 5 43. 0 40. 5 40. 5 42. 5 39. 7 43. 0 29. 4 27. 8 Fines, wt.percent 0 0 0 0 2.- 9 2. 9 2. 9 2. 9 2. 9 Run Data:

Time, hrs s 3 a 3 3 3 2% 2% Ooker Temp, F 950 930 930 930 925 925 0 900925 Pressure p.s.i.g

Data: 1

32 33 30 30 33 33 33 30 30' Yield Coke, wt. percent" 9.0 9311.4 9. 412.3 12. 4 1Q.916.017.0 Distillate, Wt. perccn 1 76. 0 72. 0 74. 4 '74.2 70.8 72 5 72. 8 69. 7 69. 2 Volatile Matterraw coke 9. 4 5. 7 13.210.8 11.8 16.2 5. 8

EXAMPLE 2 were conducted substantially as shown employing a feedcomprising a blend of and vacuum reduced residuum in the ratio Threetest runs in the drawing, Duo-Sol extract of 0.19 to 1.0 and having thefollowing properties:

Gravity, A.P.I 16.5 HP 460 5% 680 10% 770 20% 870 30% 9 15 40% 947 50%975 60% 1000 S.S.U. at 210 F 262 Sulfur, wt. percent 0.74 C.C.R., wt.percent 6.61

During this run partially-wet coke fines from the water settling pit(which had been previously separated and then drained) were slurriedwith gas oil to provide a 22 wt.. percent slurry, which was injecteddirectly into the coke drums as shown in the drawing. While injectingfines thetfurnace transfer temperature of the heater charge was raised20 F. above normal to affect the quenching effectv of the cold gas oiland coke fines.

Table 11 shows material balances and operating data for the three testruns. The gas oil used in the slurry is not shown as a charge because itwas just a small recycle stream within the cokcr.

Table [1 MATERIAL BALANCE AND COKER OPERATING DATA COKE FINES INJECTIONTEST RUNS Run I Run II Run III d BPD LV, Lbs/Hr. Wt. BPD LV, Lbs/Hr. Wt.BPD LV, Lbs/Hr. Wt

percent percent percent percent percent percent Charge:

Fresh Feed 9,148 99. 127, 805 98. 7 8, 002 99. 2 111,104 98. 9 7, 63909.1 107,194 98. 9 Coke Fines (B1 015) 1 (96) 1.0 1, 607 1.3 (72) 0.81,250 1.1 (72) 0. 9 1.250 1.1 Total 9, 244 100.0 129, 472 100 0 8,074100.0 112, 414 100.0 7,701 100.0 108, 444 100.0

Yield:

Gas (BFOE) (1, 099) 11. 8 12,386 9.5 (1,225) 15. 2 14, 429 12.8 (1,205)15.5 14,190 13. 0 Gasoline 2, 000 21. 6 21,883 16.9 1, 783 22.1 19, 42717. 2 ,685 21. 7 18, 436 17. 0 Naphtha. 781 8.5 9, 353 7. 3 600 7. 5 7,245 6. 4 625 8. 0 7, 567 7.0 Gas Oil... 4, 929 53. 4 64, 323 49. it 3,363 41. 6 43, 971 39. 2 3, 348 43. 2 43, 565 40. 2 Coke (BFOE) 1 (1,356) 14. 6 3,475 18. 2 (1, 332) 16.4 23,075 20.6 (1, 284) 16. 5 22, 23220. 5 021 9. 9 1,948 1. 5 229 2. 8 4, 297 3. 8 386 3. 9 2, 454 2.3

7, 761 108, 444 ,fl fl Heater Charge, BPD 10,000 Recycle R 0.3 FurnaceTransler 2 40- Fl rnace Tr nsler,

2 925 935 Alter 20 l1rs 940 Coke Drum Outlet, Temperature,

BFOE Goke=1 ton coke.

1 Conversion factor used: 4.812 Z The lower figure would apply Table 111gives the total quantity of fines injected and total coke producedduring the three test runs.

Table III Fines Injected Run Coke Made (Tons) Tons Tons per hr. f,

Friability tests conducted upon the raw coke showed that the injectionof fines had no adverse effect upon the strength of the coke produced.

EXAMPLE 3 Sustained operations were conducted in accordance with theprocess shown in the drawing, employing a mixed feed of the same type asthat of Example 2 and typically having about the same properties. Duringa period of six months of such continuous operations, the hot cyclonefines charged amounted to about 54 wt. percent of the fines produced orabout 0.6% of the coker feed, reducing the net fine production fromabout 5.4 wt. percent of the average coke production before commencementof fines injection, to about 2.5 wt. percent of the average cokeproduction during the period of fines injection.

During these operations it was found that it the fines were injectedthroughout the entire drum cycle, so that the fines injected late in thecycle did not become cemented into the coke mass, they Were stillpresent when the drum was opened. This difiiculty can be improved byinjecting the fines at a greater rate during the early part of the cycleand then discontinuing the injection during the latter part of thecycle.

Just prior to the six-month period mentioned above, a short period ofoperation was carried out in which the coke fines were slurried intonormal feed stock and charged to the unit thru line 1 (refer todrawing). In this particular unit fluid velocities in the furnace feedpump at the start of the 24-hour run and gradually work up to the higherfigure by the end 01 the run.

and thet furnace tubes of the unit proved to be excessive causing severeerosion at these points. Otherwise this method of operations proved tobe entirely satisfactory. Mechanical redesign of these two pieces ofequipment using Widely known engineering skills could have correctedthis erosion problem, but in this particular case it proved to be moredesirable to change to the method of operation described in the firstportion of this Example 3.

I claim:

1. In a process for the production of petroleum coke by the delayedcoking method comprising the steps of introducing a heavy petroleumresiduum into the bottom of a coking drum, subjecting said residuum todelayed coking conditions of temperature and pressure to thermallydecompose said residuum to produce a mass of solid raw coke filling thecoking drum, removing the raw coke from the drum, calcining said rawcoke, and recovering the coke fines produced during the calcining step,the improvement which comprises injecting the recovered coke fines intothe coker feed during the coking step.

2. The process of claim 1 further wherein the coke fines are slurried ina hydrocarbon oil prior to injection into the coker feed.

3. The process of is gas oil.

4. In a process for the production of petroleum coke by the delayedcoking method comprising the steps of introducing a heavy petroleumresiduum into the bottom of a coking drum, subjecting said residuum todelayed coking conditions of temperature and pressure to thermallydecompose said residuum to produce a mass of solid raw coke filling thecoking drum, removing the raw coke from the drum, recovering the cokefines produced during the step of removing the coke from the drum, theimprovement which comprises injecting the recovered coke fines into thecoker feed during the coking step.

5. The process of claim 4 wherein the raw coke is removed from the cokedrum by means of high impact-producing jets of water.

6. The process of claim 5 wherein the coke fines are slurried in ahydrocarbon oil prior to injection into the coker feed.

claim 2 in which the hydrocarbon oil 7. The process of 0121 slurried ingas oil prior im 5 wherein the coke fines are to injection into thecoker feed.

References Cited in the file of this patent UNITED STATES PATENTS WatsonMar. 17, 1931 Egioff Mar. 30, 1943 Meyers Feb. 8, 1944 Chaney et a1.Jan. 8, 1957 Boston Nov. 19, 1957 Spencer Sept. 16, 1958 Hackley Jan.26, 1960

1. IN A PROCESS FOR THE PRODUCTION OF PETROLEUM COKE BY THE DELAYEDCOKING METHOD COMPRISING THE STEPS OF INTRODUCING A HEAVY PETROLEUMRESIDUUM INTO THE BOTTOM OF A COKING DRUM, SUBJECTING SAID RESIDUUM TODELAYED COKING CONDITIONS OF TEMPERATURE AND PRESSURE TO THERMAL LYDECOMPOSE SAID RESIDUUM TO PRODUCE A MASS OF SOLID RAW COKE FILLING THECOKING DRUM, REMOVING THE RAW COKE FROM THE DRUM, CALCINING SAID RAWCOKE, AND RECOVERING THE COKE FINES PRODUCED DURING THE CALCINING STEP,THE IMPROVEMENT WHICH COMPRISES INJECTING THE RECOVERED COKE FINES INTOTHE COKER FEED DURING THE COKING STEP.